Thick film silver compositions useful as silver terminations for reduced barium titanate (RBT) capacitors are old in the art.
In general, such silver compositions contain silver powder, glass, organic vehicle and, optionally, certain inorganic materials such as cuprous oxide, bismuth oxide which function, for example, as adhesion promoters. One such composition, available commercially, contains 70.4% by weight of silver, 2% by weight of glass, 2% by weight of cuprous oxide, the remainder being an organic vehicle. Another such composition, also available commercially, contains 57% by weight of silver, 7% by weight of glass, and 26% by weight of vehicle. These compositions, however, yield capacitors having capacitance density lower than required for certain applications.
Other commercially available silver compositions, useful for terminating RBT capacitors, produce capacitors of widely varying properties when fired between 750.degree.-950.degree. C. Some of the dielectric properties of these capacitors are shown below and serve as a basis for showing the need for improved termination compositions.
______________________________________ Voltage DF.sup.b Max. CD.sub.2.sup.c Max. IR.sup.d Capacitor.sup.a (volts DC) (% max.) (nF/in.sup.2) (mega ohm) ______________________________________ Centralab Ultra-Kap (I and II) 16 7.sup.e 625.sup.e &lt;10 RMC Magna- caps 12 5.sup.f 934.sup.f &lt;10 Erie Trans- caps 25 10.sup.g 338.sup.g &lt;100 Sprague "Hypercon" 16 -- 554.sup.e &lt;100 ______________________________________ .sup.a RBT body terminated with commercial silver compositions .sup.b Dissipation factor .sup.c Maximum capacitance density .sup.d Maximum insulation resistance, measured at the working voltage .sup.e Tested at 0.1 volt root mean square (RMS), 1 KHz, 25.degree. C. .sup.f Tested at 0.05 volt RMS, 1 KHz, 25.degree. C. .sup.g Tested at 0.075 volt RMS, 1 KHz, 25.degree. C.